The present invention relates to the microgrippers, particularly to shape memory polymer gripper/release mechanisms, and more particularly to a method and apparatus for loading shape memory gripper mechanisms.
In recent years, substantial research and development has been directed to microactuators, microgrippers, etc. particularly for medical applications and capable of operating in 250-500 .mu.m diameter applications, such as the blood vessels in the human body. Recently a shape memory polymer (SMP) material has been developed wherein above a certain temperature (Tc) the material becomes soft and can be shaped by applying pressure, and cooling to a temperature below Tc, and upon reheating the material to a temperature above Tc the material returns to its original shape.
By the use of the SMP material, microgrippers have been developed for applications such as depositing material (i.e., embolic coils) in the blood vessels. Due to the capability of the SMP materials, a small SMP tube attached to a guide wire or catheter is heated, an embolic coil, for example, is inserted in the tube, and pressure is applied to the SMP material causing it to conform about the coil, whereafter the SMP material is cooled thereby freezing the SMP material in the formed shape thereby gripping the coil, and upon reheating the SMP material the material returns to its original shape thereby releasing the coil. Such SMP microgrippers are described and claimed in copending U.S. application Ser. No. 08/807,412 filed Feb. 28, 1997, entitled, "Microfabricated Therapeutic Actuators", and assigned to the same assignee, now U.S. Pat. No. 5,911,737 issued Jun. 15, 1999.
The present invention involved the loading of the SMP tubing with deposit material for medical applications, such as an embolic coil, medication, etc., and for non-medical applications requiring the delivery and release of components in normally inaccessible areas. The apparatus of the present invention operates via differential pressure between vacuum and hydrostatic water pressure whereby an application of uniform pressure on the exterior of the SMP tubing, with a vacuum on the interior thereof causes heated SMP tubing to change shape and grip a device located therein, after which the SMP tubing is cooled and thereby freezes in its changed shape. The heating and the cooling of the SMP tubing can be accomplished by the water utilized to produce the pressure for changing the shape of the SMP tubing. The heating of the SMP tubing may also be accomplished using optical fibers and laser light. Also, either heated water passing through a catheter to which the SMP tubing is attached or laser light via optical fibers packed to the SMP tubing may be utilized to reheat the tubing and release the device therefrom.